Private investigators hired by the family of Canadian billionaires Barry and Honey Sherman believe the couple were murdered by multiple killers in December, and did not die as the result of a murder-suicide, CBC reports.

The children of the Shermans never believed the murder-suicide theory, releasing a statement after their parents' bodies were found on Dec. 15 that such a theory, which had been forth by a source in the Toronto police, added up to nothing more that "rumors regrettably circulated." In response, the family hired a team of independent investigators, including several former Toronto homicide detectives, to determine what happened to their parents, whose bodies were found hanging by the pool in their Toronto mansion.

A source with knowledge of that team's investigation says there are several pieces of evidence pointing in the direction of multiple killers.

For one, claims the source, investigators have discovered evidence that both of the victims had their necks wrapped with leather belts.

Those belts were then tied to a handrail. In addition, there is evidence that the couple was bound together at the wrists at some point, though no rope or wire was found on the crime scene, reports the International Business Times.

The team has also come to believe that Barry and Honey were killed two days before their bodies were found, on Dec. 13, based on the fact the fact that Honey was wearing the same outfit she was in on that day.

Investigators also believe Honey Sherman struggled with her killers, as she was found with cuts on her lips and nose.